mrptb2:
When you say "sounds like overkill" do you mean a simple 24 gauge pair (or however many wires are needed) would usually work for something like this?
Thinking about it some more, you probably need to supply power, so you need at least 4 cores. Probably at that rate the twisted pair is not a bad idea, as you could always add in the RS485 chips later, even if you don't at the start.